Fix crashes when calling sourcesAtFrame when clearing

[rogernelson]

Fix crash calling sourcesAtFrame at session clear.

Summarize your change.

If sourcesAtFrame is called in an event from which the graph is cleared (graph-node-inputs-changed in my case, but it could be anything that clears the graph), RV will crash with a stack resembling the below:

* thread #1, name = 'RV Main', queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x793bcc0f30f4744a)
  * frame #0: 0x00000001003e8688 RV`IPCore::AdaptorIPNode::metaEvaluate(this=0x0000000a96080780, c=0x000000016fdf6290, visitor=0x000000016fdf6c40) at AdaptorIPNode.cpp:92:31
    frame #1: 0x000000010027b920 RV`IPCore::IPNode::metaEvaluate(this=0x0000000a96080a00, context=0x000000016fdf6290, visitor=0x000000016fdf6c40) at IPNode.cpp:408:23
    frame #2: 0x000000010027b920 RV`IPCore::IPNode::metaEvaluate(this=0x0000000a96074000, context=0x000000016fdf6290, visitor=0x000000016fdf6c40) at IPNode.cpp:408:23
    frame #3: 0x00000001007d5eb0 RV`IPCore::RetimeIPNode::metaEvaluate(this=0x0000000a96074000, context=0x000000016fdf6378, visitor=0x000000016fdf6c40) at RetimeIPNode.cpp:661:17
    frame #4: 0x00000001007e1790 RV`IPCore::StackIPNode::metaEvaluate(this=0x0000000a94a2f100, context=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at StackIPNode.cpp:791:25
    frame #5: 0x000000010027b920 RV`IPCore::IPNode::metaEvaluate(this=0x0000000a9320d500, context=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at IPNode.cpp:408:23
    frame #6: 0x000000010040cefc RV`IPCore::GroupIPNode::metaEvaluate(this=0x0000000a95bf2080, c=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at GroupIPNode.cpp:114:25
    frame #7: 0x00000001003e8690 RV`IPCore::AdaptorIPNode::metaEvaluate(this=0x0000000a94774a00, c=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at AdaptorIPNode.cpp:92:31
    frame #8: 0x00000001003e8690 RV`IPCore::AdaptorIPNode::metaEvaluate(this=0x0000000a94cf8c80, c=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at AdaptorIPNode.cpp:92:31
    frame #9: 0x000000010040cefc RV`IPCore::GroupIPNode::metaEvaluate(this=0x0000000a95bf0500, c=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at GroupIPNode.cpp:114:25
    frame #10: 0x000000010027b920 RV`IPCore::IPNode::metaEvaluate(this=0x0000000a8cd01500, context=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at IPNode.cpp:408:23
    frame #11: 0x000000010027b920 RV`IPCore::IPNode::metaEvaluate(this=0x0000000a95bf0280, context=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at IPNode.cpp:408:23
    frame #12: 0x000000010040cefc RV`IPCore::GroupIPNode::metaEvaluate(this=0x0000000a95bf0a00, c=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at GroupIPNode.cpp:114:25
    frame #13: 0x00000001003e8690 RV`IPCore::AdaptorIPNode::metaEvaluate(this=0x0000000a94cf8780, c=0x000000016fdf67f0, visitor=0x000000016fdf6c40) at AdaptorIPNode.cpp:92:31
    frame #14: 0x00000001003f4a40 RV`IPCore::DisplayStereoIPNode::metaEvaluate(this=0x0000000a95437480, context=0x000000016fdf69d0, visitor=0x000000016fdf6c40) at DisplayStereoIPNode.cpp:393:20
    frame #15: 0x00000001003e8690 RV`IPCore::AdaptorIPNode::metaEvaluate(this=0x0000000a947bd180, c=0x000000016fdf69d0, visitor=0x000000016fdf6c40) at AdaptorIPNode.cpp:92:31
    frame #16: 0x000000010027b920 RV`IPCore::IPNode::metaEvaluate(this=0x0000000a95b96800, context=0x000000016fdf69d0, visitor=0x000000016fdf6c40) at IPNode.cpp:408:23
    frame #17: 0x000000010040cefc RV`IPCore::GroupIPNode::metaEvaluate(this=0x0000000a95bf0f00, c=0x000000016fdf69d0, visitor=0x000000016fdf6c40) at GroupIPNode.cpp:114:25
    frame #18: 0x00000001003ee27c RV`IPCore::DisplayGroupIPNode::metaEvaluate(this=0x0000000a93e41500, context=0x000000016fdf6bb8, visitor=0x000000016fdf6c40) at DisplayGroupIPNode.cpp:425:21
    frame #19: 0x000000010027b920 RV`IPCore::IPNode::metaEvaluate(this=0x0000000a94774780, context=0x000000016fdf6bb8, visitor=0x000000016fdf6c40) at IPNode.cpp:408:23
    frame #20: 0x00000001006ce2b4 RV`IPMu::sourcesAtFrame(node_=0x000000013a849440, thread_=0x0000000117748e00) at CommandsModule.cpp:1937:28
    frame #21: 0x0000000100e7a890 RV`Mu::DynamicArrayType::nodeEval(this=0x00000001176fcdc0, n=0x000000013a849440, thread=0x0000000117748e00) const at DynamicArrayType.cpp:78:90
    frame #22: 0x0000000100076e80 RV`Mu::Node::eval(this=0x000000013a849440, t=0x0000000117748e00) const at Node.cpp:142:62
    frame #23: 0x00000001000a92ac RV`Mu::Thread::call(this=0x0000000117748e00, f=0x0000000117e86d20, args=size=1, returnArguments=false) at Thread.cpp:422:23
    frame #24: 0x00000001001d2e2c RV`TwkApp::MuSymbol_call(_self=0x000000011b52a7f0, args=0x000000030a0d8bb0, kwds=0x0000000000000000) at PyMuSymbolType.cpp:389:48
    frame #25: 0x0000000108d17350 libpython3.11.dylib`_PyObject_MakeTpCall(tstate=0x00000001090a3c30, callable=0x000000011b52a7f0, args=<unavailable>, nargs=<unavailable>, keywords=0x0000000000000000) at call.c:214:18 [opt]
    frame #26: 0x0000000108d17850 libpython3.11.dylib`PyObject_Vectorcall [inlined] _PyObject_VectorcallTstate(tstate=<unavailable>, callable=<unavailable>, args=<unavailable>, nargsf=<unavailable>, kwnames=<unavailable>) at pycore_call.h:90:16 [opt] [artificial]
    frame #27: 0x0000000108df4dc0 libpython3.11.dylib`_PyEval_EvalFrameDefault(tstate=<unavailable>, frame=0x000000010a6f01d8, throwflag=<unavailable>) at ceval.c:0 [opt]
    frame #28: 0x0000000108df05fc libpython3.11.dylib`_PyEval_Vector [inlined] _PyEval_EvalFrame(tstate=0x00000001090a3c30, frame=0x000000010a6f01d8, throwflag=0) at pycore_ceval.h:73:16 [opt]
    frame #29: 0x0000000108df05ec libpython3.11.dylib`_PyEval_Vector(tstate=0x00000001090a3c30, func=<unavailable>, locals=<unavailable>, args=<unavailable>, argcount=<unavailable>, kwnames=<unavailable>) at ceval.c:6434:24 [opt]
    frame #30: 0x0000000108d19f24 libpython3.11.dylib`method_vectorcall [inlined] _PyObject_VectorcallTstate(tstate=0x00000001090a3c30, callable=0x000000013792e7a0, args=0x000000016fdf7ab0, nargsf=<unavailable>, kwnames=0x0000000000000000) at pycore_call.h:92:11 [opt]
    frame #31: 0x0000000108d19efc libpython3.11.dylib`method_vectorcall(method=<unavailable>, args=0x000000030a0d8268, nargsf=<unavailable>, kwnames=0x0000000000000000) at classobject.c:89:18 [opt]
    frame #32: 0x00000001001cf9d4 RV`TwkApp::PyFunctionAction::execute(this=0x0000000a8fade490, d=0x0000000a912c6000, event=0x000000016fdf7f28) const at PyFunctionAction.cpp:58:17
    frame #33: 0x00000001006612a8 RV`TwkApp::Document::executeAction(this=0x0000000a912c6000, event=0x000000016fdf7f28) at Document.cpp:486:20
    frame #34: 0x0000000100661b7c RV`TwkApp::Document::receiveEvent(this=0x0000000a912c6000, event=0x000000016fdf7f28) at Document.cpp:613:9
    frame #35: 0x000000010066fc38 RV`TwkApp::EventNode::propagateEvent(this=0x0000000a912c6000, event=0x000000016fdf7f28) at EventNode.cpp:71:13
    frame #36: 0x00000001001ecd94 RV`IPCore::Session::propagateEvent(this=0x0000000a912c6000, event=0x000000016fdf7f28) at Session.cpp:4644:43
    frame #37: 0x000000010066fca8 RV`TwkApp::EventNode::propagateEvent(this=0x0000000a909c9800, event=0x000000016fdf7f28) at EventNode.cpp:82:24
    frame #38: 0x000000010066fc00 RV`TwkApp::EventNode::sendEvent(this=0x0000000a909c9800, event=0x000000016fdf7f28) at EventNode.cpp:60:16
    frame #39: 0x000000010038b604 RV`IPCore::IPGraph::inputsChanged(this=0x0000000a909c9800, n=0x0000000a8d8b2800) at IPGraph.cpp:3449:13
    frame #40: 0x000000010027af8c RV`IPCore::IPNode::setInputs(this=0x0000000a8d8b2800, nodes=size=0) at IPNode.cpp:303:26
    frame #41: 0x0000000100279c4c RV`IPCore::IPNode::removeInput(this=0x0000000a8d8b2800, n=0x0000000a94a30500) at IPNode.cpp:166:13
    frame #42: 0x000000010027984c RV`IPCore::IPNode::~IPNode(this=0x0000000a94a30500) at IPNode.cpp:57:32
    frame #43: 0x000000010040c900 RV`IPCore::GroupIPNode::~GroupIPNode(this=0x0000000a94a30500) at GroupIPNode.cpp:48:5
    frame #44: 0x0000000100807490 RV`IPCore::SwitchGroupIPNode::~SwitchGroupIPNode(this=0x0000000a94a30500) at SwitchGroupIPNode.cpp:42:5

Notice the destructors are triggering a sourcesAtFrame call, which then tries to access those same objects being destroyed resulting in a use-after-free crash.

To fix this, we'll set a guard when the graph is being cleared, and if sourcesAtFrame is called when the guard is set, we'll return an empty array. This is the as what would happen if you called sourcesAtFrame when there were no sources (ie after the graph was cleared). So we'll just return the eventual result early, which is likely what the users want anyway, and this will protect python events from crashing RV.

Describe the reason for the change.

Prevent crashes

Describe what you have tested and on which operating system.

Mac OS 26.2

[bernie-laberge]

Beautiful
Thank you @rogernelson !